The ganglioside content and composition of growth cones prepared from forebrains of day 0 (p0), day 2 (p2), and day 6 (p6) postnatal rats was analysed in comparison with that of whole forebrain membranes obtained from rats of the same age. The amount of total ganglioside bound sialic acid (microgram NeuAc mg protein-1) was found to increase in both whole cerebrum membranes and growth cones from p0 to p6. The ganglioside concentrations of growth cones exceeded that of the whole cerebrum by 35-40% at all time points investigated. The major rat brain gangliosides were also found in the growth cone fractions, however, in different relative amounts. Thus, the well known developmental shift from the b- to the a-ganglioside synthesis pathway was significantly delayed in growth cones, indicating that this shift is not associated with axonal growth but more likely with the subsequent period of synaptogenesis. GQ1c, recognized by the mAb Q211, and an unidentified growth-cone specific ganglioside x were found to be expressed in growth cones of p0 rats and to decrease up to p6.